Motor cooling method and motor control device

Abstract

To effectively cool a motor even when an electric vehicle continues traveling with a high load.SOLUTION: In an oil cooling circuit (11) provided with a water-cooled oil cooler (27) and an air-cooled oil cooler (35), a motor control device (3) circulates the oil in the oil cooling circuit (11) only to the water-cooled oil cooler (27) when the temperature of a rear motor (26) is lower than a predetermined switching temperature, and circulates the oil in the oil cooling circuit (11) to the water-cooled oil cooler (27) and the air-cooled oil cooler (35) when the temperature of the rear motor (26) is higher than or equal to the switching temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a motor cooling method and a motor control device. [Background technology]

[0002] Conventionally, an electric vehicle equipped with a first motor and a second motor, in which the output of each motor is controlled according to the temperature of each motor, is disclosed in Patent Document 1. In the electric vehicle disclosed in Patent Document 1, the outputs of the first motor and the second motor are controlled so that the output torque of the motor with a relatively higher temperature is smaller than the output torque of the other motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-74655 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the conventional electric vehicle described above, the output of the motor with the higher temperature is simply reduced and the output of the motor with the lower temperature is simply increased, so if the electric vehicle continues to run at a higher load, the temperatures of both motors may rise and reach the output limit temperature.In other words, in conventional electric vehicles, because the motor output is simply adjusted, there is a problem in that the motors cannot be cooled effectively if the electric vehicle continues to run at a high load.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a motor cooling method and apparatus that can effectively cool the motor even when an electric vehicle continues to run under high load. [Means for solving the problem]

[0006] In one aspect of the present invention, a motor cooling method and device circulates oil in the oil cooling circuit that cools the rear motor only through a water-cooled oil cooler when the temperature of the rear motor is below a predetermined switching temperature, and circulates oil in the oil cooling circuit through both the water-cooled oil cooler and the air-cooled oil cooler when the temperature of the rear motor is above the switching temperature. [Effects of the Invention]

[0007] According to the present invention, the motor can be effectively cooled even when the electric vehicle continues to run under high load. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram showing the configuration of a motor cooling system including a motor control device according to one embodiment. [Figure 2] FIG. 2 is a top view of the electric vehicle for explaining the arrangement of the air-cooled oil cooler. [Figure 3] FIG. 3 is a side view of the electric vehicle for explaining the arrangement of the air-cooled oil cooler. [Figure 4] FIG. 4 is a diagram for explaining the cooling path in the rear power train. [Figure 5] FIG. 5 is a diagram for explaining a method for setting the switching temperature by the motor control device according to one embodiment. [Figure 6] FIG. 6 is a flowchart showing the procedure of the motor cooling process performed by the motor control device according to one embodiment. [Figure 7] FIG. 7 is a diagram for explaining an example of a motor cooling process performed by a motor control device according to an embodiment. [Figure 8] FIG. 8 is a diagram for explaining a method for changing the driving force distribution by a motor control device according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] A motor cooling method and a motor control device according to this embodiment will be described below with reference to the drawings. In the description of the drawings, the same parts are given the same reference numerals and the description will be omitted.

[0010] [Motor cooling system configuration] The configuration of a motor cooling system equipped with a motor control device according to this embodiment will be described with reference to Figure 1. Figure 1 is a block diagram showing the configuration of the motor cooling system according to this embodiment. As shown in Figure 1, motor cooling system 1 includes a motor control device 3, a front powertrain 5, a rear powertrain 7, a water cooling circuit 9, an oil cooling circuit 11, a front temperature sensor 13, and a rear temperature sensor 15. Motor cooling system 1 is also connected to a navigation device 17.

[0011] The motor cooling system 1 is mounted on an electric vehicle and cools the front powertrain 5 and rear powertrain 7 with a water cooling circuit 9 and an oil cooling circuit 11. In Fig. 1, it is shown as if only the rear powertrain 7 is provided with the oil cooling circuit 11, but the front powertrain 5 is also provided with an oil cooling circuit.

[0012] The front powertrain 5 is a powertrain that drives the front wheels of the electric vehicle and includes a front inverter 21, a front motor 22, a front water-cooled oil cooler 23, and a front gearbox 24. The front inverter 21 converts DC power supplied from a battery into AC power and supplies it to the front motor 22. The front motor 22 drives the front wheels of the electric vehicle using the AC power supplied from the front inverter 21. The front water-cooled oil cooler 23 is cooled by cooling water in a water-cooled circuit 9 that cools the front powertrain 5 and the rear powertrain 7, and cools oil in an oil-cooled circuit (not shown) of the front powertrain 5. The front gearbox 24 houses a transmission driven by the front motor 22.

[0013] Similarly, the rear powertrain 7 is a powertrain that drives the rear wheels of the electric vehicle, and includes a rear inverter 25, a rear motor 26, a water-cooled oil cooler 27, and a rear gearbox 28. The rear inverter 25 converts DC power supplied from the battery into AC power and supplies it to the rear motor 26. The rear motor 26 drives the rear wheels of the electric vehicle using the AC power supplied from the rear inverter 25. The water-cooled oil cooler 27 is cooled by cooling water in a water-cooled circuit 9 that cools the front powertrain 5 and the rear powertrain 7, and cools oil in an oil-cooled circuit 11 of the rear powertrain 7. The rear gearbox 28 houses a transmission driven by the rear motor 26.

[0014] The water-cooled circuit 9 cools the entire electric vehicle by circulating coolant through the front powertrain 5 and the rear powertrain 7. The water-cooled circuit 9 includes a pump 31, a reservoir tank 32, and a radiator 33. The coolant stored in the reservoir tank 32 is circulated by the pump 31, and heat is dissipated by the radiator 33.

[0015] The oil cooling circuit 11 circulates oil within the rear powertrain 7 to cool various parts of the rear powertrain 7, and in particular cools the rear motor 26. The oil cooling circuit 11 includes an air-cooled oil cooler 35 and a bypass valve 36, and by switching the bypass valve 36, oil is circulated to the water-cooled oil cooler 27 and the air-cooled oil cooler 35. Therefore, the oil cooling circuit 11 is provided with the water-cooled oil cooler 27 and the air-cooled oil cooler 35 as radiators. Although not shown, the front powertrain 5 is also provided with an oil cooling circuit, but is not provided with an air-cooled oil cooler.

[0016] The front temperature sensor 13 detects the temperature inside the rotor, stator, etc. of the front motor 22. The rear temperature sensor 15 detects the temperature inside the rotor, stator, etc. of the rear motor 26. The navigation device 17 searches for a route to the destination of the electric vehicle.

[0017] The motor control device 3 is an ECU (electronic control unit) that is mounted on an electric vehicle and controls the motor that drives the electric vehicle. The motor control device 3 controls the driving of the front motor 22 and the rear motor 26, and also performs a cooling process to prevent the temperature of the front motor 22 and the rear motor 26 from rising. The motor control device 3 includes a control unit 41 and a memory unit 43.

[0018] The control unit 41 is a controller that controls the motor that drives the electric vehicle, and cools the rear motor 26 by switching the bypass valve 36 to circulate oil through the water-cooled oil cooler 27 and the air-cooled oil cooler 35. The control unit 41 also changes the distribution of driving force between the front motor 22 and the rear motor 26 according to the temperatures of the front motor 22 and the rear motor 26.

[0019] Specifically, when the temperature of the rear motor 26 is below a predetermined switching temperature, the control unit 41 circulates the oil in the oil cooling circuit 11 only through the water-cooled oil cooler 27. On the other hand, when the temperature of the rear motor 26 is equal to or higher than the switching temperature, the control unit 41 circulates the oil in the oil cooling circuit 11 through the water-cooled oil cooler 27 and the air-cooled oil cooler 35.

[0020] The memory unit 43 is a memory or database that records the information necessary to execute the motor cooling process, such as various parameters such as the switching temperature and the distribution change temperature, as well as the weight and size of the input towing vehicle.

[0021] The motor control device 3 is a computer configured with general-purpose electronic circuits including a microcomputer, microprocessor, and CPU, as well as peripheral devices such as memory, and is installed with a computer program for executing the motor cooling process. Each function of the motor control device 3 can be implemented by one or more processing circuits. The processing circuit may include, for example, a programmed processing device including electrical circuits, and may also include devices such as application-specific integrated circuits (ASICs) or conventional circuit components arranged to perform the functions described in the embodiments.

[0022] [Air-cooled oil cooler placement] Next, the arrangement of the air-cooled oil cooler 35 will be described with reference to Figures 2 and 3. Figure 2 is a view of the electric vehicle as seen from above, and Figure 3 is a view of the electric vehicle as seen from the side. As shown in Figures 2 and 3, the rear powertrain 7 is disposed behind the battery 50, and rear tires 51 are disposed on both sides of the rear powertrain 7.

[0023] In an electric vehicle arranged in this manner, the air-cooled oil cooler 35 is installed rearward of the rear powertrain 7 including the rear motor 26. The air-cooled oil cooler 35 takes in traveling wind from a side body 52 on the side of the electric vehicle shown in Fig. 2 and is cooled by the taken-in traveling wind. The air-cooled oil cooler 35 also takes in traveling wind from an undercover 53 on the bottom surface of the electric vehicle shown in Fig. 3 and is cooled by the taken-in traveling wind.

[0024] By installing the air-cooled oil cooler 35 behind the rear motor 26 in this way, the rear motor 26 is not affected by the heat dissipation from the air-cooled oil cooler 35, and it is possible to efficiently cool the rear powertrain 7. Furthermore, because heat can be dissipated at the rear of the electric vehicle, it is possible to reduce the heat dissipation load of the radiator 33 installed at the front of the electric vehicle, and it is possible to reduce the size of the radiator 33.

[0025] [Switching the cooling path of the oil cooling circuit] Next, a method for switching the cooling path of the oil cooling circuit 11 will be described with reference to Fig. 4. Fig. 4 is a diagram for explaining the cooling path within the rear powertrain 7. As shown in Fig. 4, in the oil cooling circuit 11, oil discharged from the oil pump 37 is sent to the air-cooled oil cooler 35 or the water-cooled oil cooler 27 by a bypass valve 36. The oil that has dissipated heat in these oil coolers circulates through the rear gearbox 28 and the rear motor 26 and is collected in a tank 38.

[0026] Here, when the temperature of the rear motor 26 is below the switching temperature, the control unit 41 switches the bypass valve 36 so that oil does not flow to the air-cooled oil cooler 35, and circulates oil only through the water-cooled oil cooler 27.

[0027] As a result, when the rear powertrain 7 is cold, the oil temperature rises and friction in the rear gearbox 28 is reduced, improving electricity consumption. In addition, the heat loss generated by the rear motor 26 is recovered by the oil, and the recovered heat is exchanged with the coolant in the water-cooled oil cooler 27, thereby warming up the coolant and making effective use of it for heating the interior of the vehicle (promoting warm-up).

[0028] On the other hand, when the temperature of the rear motor 26 reaches or exceeds the switching temperature, the control unit 41 switches the bypass valve 36 so that the oil flows to the air-cooled oil cooler 35, and circulates the oil through the water-cooled oil cooler 27 and the air-cooled oil cooler 35.

[0029] As a result, when cooling of the rear powertrain 7 is required, the cooling capacity of both the air-cooled oil cooler 35 and the water-cooled oil cooler 27 can be utilized, thereby enhancing the cooling capacity and improving reliability. Also, by cooling in the order of the air-cooled oil cooler 35 first and the water-cooled oil cooler 27, efficient cooling is possible.

[0030] [How to set the switching temperature] Next, a method for setting the switching temperature for switching the bypass valve 36 will be described with reference to FIG. 5. FIG. 5 is a diagram showing the relationship between oil temperature and friction in the transmission inside the gearbox. In the transmission inside the gearbox, there is friction due to meshing friction between the gears, and as shown in FIG. 5, this friction is sensitive to the drive load (rotation speed x torque) and the temperature of the oil circulating inside. In other words, when the oil temperature is low, friction increases even with the same drive load, and more drive force is required. This leads to worsening fuel efficiency in electric vehicles and a reduced cruising range.

[0031] Therefore, the switching temperature is set at the boundary temperature between the range in which friction changes and the range in which friction remains stable. For example, as shown in Fig. 5, a switching temperature Tx is set for each of the drive loads A to C. The switching temperature Tx is set at the boundary temperature between the range in which transmission friction increases as the transmission oil temperature decreases and the range in which friction does not change even if the transmission oil temperature increases.

[0032] Therefore, for each of the drive loads A to C, when the temperature is in the range below the switching temperature Tx, the bypass valve 36 is activated to prevent oil from circulating in the air-cooled oil cooler 35. This prevents heat from being released to the outside, promotes warm-up, and prevents an increase in friction in the transmission due to a drop in oil temperature.

[0033] On the other hand, in the range above the switching temperature Tx, the bypass valve 36 is turned OFF to circulate the oil through the air-cooled oil cooler 35. As a result, when cooling is required due to a rise in oil temperature, cooling can be performed by both the air-cooled oil cooler 35 and the water-cooled oil cooler 27, thereby enhancing the cooling capacity.

[0034] [Motor cooling treatment] Next, the motor cooling process performed by the motor control device 3 according to this embodiment will be described with reference to Figures 6 and 7. Figure 6 is a flowchart showing the processing steps of the motor cooling process, and Figure 7 is a diagram for explaining an example of the motor cooling process. The motor cooling process shown in Figure 6 starts when the user turns on the power to the electric vehicle.

[0035] As shown in Fig. 6, in step S101, when the electric vehicle starts to travel, the control unit 41 sets the driving force distribution between the front motor 22 and the rear motor 26. At the start of travel, the driving force distribution between the front motor 22 and the rear motor 26 is set to 50:50, as shown in Fig. 7.

[0036] In step S103, the control unit 41 calculates the driving force of the electric vehicle. The control unit 41 acquires information such as the output torque and rotation speed of the front motor 22 and the rear motor 26, and calculates the driving force of the electric vehicle from the acquired information.

[0037] In step S105, control unit 41 determines whether the driving force calculated in step S103 is equal to or greater than a predetermined driving force threshold A, and if the driving force is equal to or greater than driving force threshold A, proceeds to step S107. On the other hand, if the driving force calculated in step S103 is less than driving force threshold A, the driving force distribution is maintained unchanged and proceeds to step S125.

[0038] In step S107, the control unit 41 determines that the driving force of the electric vehicle is equal to or greater than driving force threshold A, and therefore determines that the vehicle is running under high load, and increases the driving force distribution to the rear motor 26 relative to the driving force distribution to the front motor 22. Specifically, as shown in Fig. 8, the control unit 41 sets the driving force distribution between the front motor 22 and the rear motor 26 to 50:50 when the driving force is less than driving force threshold A, and sets the driving force distribution to 40:60 when the driving force is equal to or greater than driving force threshold A. Furthermore, the control unit 41 sets the driving force distribution between the front motor 22 and the rear motor 26 to 20:80 when the driving force of the electric vehicle is equal to or greater than driving force threshold B, which is greater than driving force threshold A.

[0039] The control unit 41 can also predict the driving load on the electric vehicle according to preset driving conditions, calculate the predicted load, and change the distribution of driving force between the front motor 22 and the rear motor 26 according to the calculated predicted load.

[0040] For example, if there is a towing vehicle, the size and weight of the towing vehicle are recorded in the memory unit 43, allowing the control unit 41 to predict the drive load of the electric vehicle in a driving situation. Furthermore, by setting a destination in the navigation device 17, the control unit 41 can obtain road conditions such as traffic congestion to the destination, average speed, arrival time on uphill roads, gradient, etc. from the navigation device 17. Therefore, the control unit 41 can predict the drive load of the electric vehicle based on the obtained road conditions.

[0041] By predicting the drive load in this way, the control unit 41 changes the drive power distribution between the front motor 22 and the rear motor 26 at the time when the predicted load changes. For example, as shown in Figure 7, at time t1, the control unit 41 predicts a transition to high-load driving and changes the drive power distribution to 40:60. However, if the drive load of the electric vehicle is predicted to be equal to or greater than drive power threshold B, the drive power distribution is changed to 20:80.

[0042] In step S109, the control unit 41 acquires the temperature of the rear motor 26 from the rear temperature sensor 15 and determines whether the acquired temperature of the rear motor 26 is below a predetermined switching temperature. If the temperature of the rear motor 26 is below the switching temperature, the process proceeds to step S111, and if the temperature is equal to or higher than the switching temperature, the process proceeds to step S113.

[0043] In step S111, since the temperature of the rear motor 26 is below the switching temperature, the control unit 41 turns on the bypass valve 36 to cause the oil in the oil cooling circuit 11 to bypass the air-cooled oil cooler 35 and circulate only through the water-cooled oil cooler 27.

[0044] In step S113, because the temperature of the rear motor 26 is equal to or higher than the switching temperature, the control unit 41 turns off the bypass valve 36, thereby circulating the oil in the oil cooling circuit 11 to both the water-cooled oil cooler 27 and the air-cooled oil cooler 35. For example, as shown in FIG. 7 , when the temperature of the rear motor 26 reaches the switching temperature Tx at time t2, the control unit 41 circulates the oil to both the water-cooled oil cooler 27 and the air-cooled oil cooler 35. As a result, after time t2, the temperature rise of the rear motor 26 is suppressed, and similarly, the temperature rise of the oil in the oil cooling circuit 11 is also suppressed.

[0045] In step S115, the control unit 41 determines whether the temperature of the front motor 22 or the rear motor 26 is equal to or higher than the output limit temperature, and if it is equal to or higher than the output limit temperature, proceeds to step S117, and if it is lower than the output limit temperature, proceeds to step S119.

[0046] In step S117, if the temperature of the front motor 22 is equal to or higher than the output limit temperature, the control unit 41 limits the output torque of the front motor 22 to the upper limit torque. On the other hand, if the temperature of the rear motor 26 is equal to or higher than the output limit temperature, the control unit 41 limits the output torque of the rear motor 26 to the upper limit torque.

[0047] In step S119, the control unit 41 determines whether the temperature of the front motor 22 or the rear motor 26 is equal to or higher than the distribution change temperature, and if it is equal to or higher than the distribution change temperature, proceeds to step S121. On the other hand, if the temperature of either the front motor 22 or the rear motor 26 is lower than the distribution change temperature, the driving force distribution is maintained without being changed, and proceeds to step S125.

[0048] In step S121, the control unit 41 determines whether the temperature of the motor other than the motor that became equal to or higher than the allocation change temperature in step S119 is below the allocation change temperature, and if it is below the allocation change temperature, the process proceeds to step S123. That is, if the temperature of either the front motor 22 or the rear motor 26 becomes equal to or higher than the allocation change temperature and the temperature of the other motor is below the allocation change temperature, the process proceeds to step S123.

[0049] On the other hand, if the temperature of the motor other than the one that has reached or exceeded the distribution change temperature is also at or above the distribution change temperature, the driving force distribution is maintained without being changed and the process proceeds to step S125. In other words, if the temperatures of both the front motor 22 and the rear motor 26 reach or exceed the distribution change temperature, the driving force distribution is maintained without being changed and the process proceeds to step S125.

[0050] In step S123, because the temperature of the front motor 22 or the rear motor 26 is equal to or higher than the distribution change temperature, the control unit 41 changes the driving force distribution between the front motor 22 and the rear motor 26. Specifically, the control unit 41 changes the driving force distribution so as to reduce the driving force distribution of the front motor 22 or the rear motor 26, whichever has its temperature rising above the distribution change temperature.

[0051] 7, at time t3, the temperature of the rear motor 26 reaches the distribution change temperature Tr, and the temperature of the front motor 22 is below the distribution change temperature Tf, so the drive power distribution between the front motor 22 and the rear motor 26 is changed from 40:60 to 50:50. Also, at time t4, the temperature of the front motor 22 reaches the distribution change temperature Tf, and the temperature of the rear motor 26 is below the distribution change temperature Tr, so the drive power distribution between the front motor 22 and the rear motor 26 is changed from 50:50 to 40:60.

[0052] In step S125, the control unit 41 determines whether the power supply to the electric vehicle has been turned off, and if the power supply to the electric vehicle has not been turned off, the process returns to step S103, and if the power supply to the electric vehicle has been turned off, the motor cooling process according to this embodiment is terminated.

[0053] [Effects of the embodiment] As explained in detail above, the motor control device 3 according to this embodiment circulates the oil in the oil cooling circuit 11 only through the water-cooled oil cooler 27 when the temperature of the rear motor 26 is below a predetermined switching temperature, and circulates the oil in the oil cooling circuit 11 through both the water-cooled oil cooler 27 and the air-cooled oil cooler 35 when the temperature of the rear motor 26 is equal to or higher than the switching temperature. As a result, when the temperature of the rear motor 26 rises, the oil can be circulated through both the water-cooled oil cooler 27 and the air-cooled oil cooler 35, so the motor can be effectively cooled even when the electric vehicle continues to run under high load.

[0054] In the water-cooling circuit 9, the thermal resistance between the inverter and the components inside the motor is large, so it is necessary to maintain a relatively low water temperature (up to 65°C). Therefore, when the outside air temperature is high (up to 45°C), it is not possible to make a difference between the air temperature and the water temperature, so it is necessary to increase the size of the radiator 33 installed in front of the electric vehicle. As a result, the vehicle's mountability decreases, making it difficult to ensure cooling performance.

[0055] In contrast, the oil-cooled parts inside the motor have a low thermal resistance because they are cooled directly by oil, and can be cooled at a relatively high oil temperature (100-120°C) compared to the guaranteed temperature of the internal parts (up to 170°C). Therefore, cooling is possible even when there is a large difference between the air temperature and the oil temperature. Therefore, in the motor cooling system 1 according to this embodiment, by adding an air-cooled oil cooler 35 to the oil cooling circuit 11, the motor can be cooled effectively without increasing the size of the radiator 33.

[0056] Furthermore, in the motor cooling system 1 according to this embodiment, the air-cooled oil cooler 35 is installed further rearward of the rear motor 26 on the electric vehicle, and is cooled by the traveling wind drawn in from the bottom or side of the electric vehicle. This means that the rear motor 26 is not affected by the heat dissipation from the air-cooled oil cooler 35, allowing for efficient cooling of the rear powertrain 7. Furthermore, because heat can be dissipated at the rear of the electric vehicle, the heat dissipation load on the radiator 33 installed at the front of the electric vehicle can be reduced, allowing the size of the radiator 33 to be reduced.

[0057] Furthermore, in the motor control device 3 according to this embodiment, the switching temperature is set to the boundary temperature between the range in which transmission friction increases as the transmission oil temperature decreases and the range in which friction does not change even if the transmission oil temperature increases. This makes it possible to control the air-cooled oil cooler 35 so that oil is not circulated below the switching temperature, thereby promoting warm-up and preventing an increase in transmission friction.

[0058] Furthermore, the motor control device 3 according to this embodiment increases the driving force allocation to the rear motor 26 compared to the driving force allocation to the front motor 22 when the driving force of the electric vehicle exceeds a predetermined driving force threshold. As a result, when the driving force of the electric vehicle increases, increasing the driving force allocation to the rear motor 26 makes it possible to use the air-cooled oil cooler 35 to reduce heat dissipation to the water-cooled circuit 9. This reduces the cooling load on the radiator 33, allowing the size of the radiator 33 to be reduced. Furthermore, because cooling of the rear motor 26 is strengthened, the cooling load on the front motor 22 can be reduced, and it is also possible to simplify the cooling structure by, for example, changing the front motor 22 to only water-cooling.

[0059] Furthermore, when the temperature of the front motor 22 or the rear motor 26 reaches or exceeds a predetermined distribution change temperature, the motor control device 3 according to this embodiment changes the drive power distribution between the front motor 22 and the rear motor 26. This allows the drive power distribution to be changed in response to the temperature rise of the front motor 22 and the rear motor 26, making it possible to suppress the temperature rise of each motor and allowing the vehicle to continue traveling even under high load.

[0060] Furthermore, in the motor cooling system 1 according to this embodiment, the water-cooled oil cooler 27 is cooled by the cooling water in the water-cooled circuit 9 that cools the front powertrain 5 having the front motor 22 and the rear powertrain 7 having the rear motor 26. As a result, the water-cooled oil cooler 27 is incorporated into the water-cooled circuit 9 that cools the entire electric vehicle, and in combination with the oil-cooled circuit 11 that cools the rear powertrain 7, the entire electric vehicle can be cooled efficiently.

[0061] Furthermore, the motor control device 3 according to this embodiment predicts the drive load on the electric vehicle according to preset driving conditions, calculates the predicted load, and changes the drive power distribution between the front motor 22 and the rear motor 26 according to the calculated predicted load. This makes it possible to predict motor temperature rises in advance even when driving under high load, allowing the vehicle to continue driving without limiting output.

[0062] Although the embodiments of the present invention have been described above, the descriptions and drawings that form part of this disclosure should not be understood to limit the present invention. Various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art from this disclosure. [Explanation of symbols]

[0063] 1 Motor cooling system 3 Motor control device 5 Front powertrain 7 Rear powertrain 9 Water cooling circuit 11 Oil cooling circuit 13 Front temperature sensor 15 Rear temperature sensor 17 Navigation devices 21 Front inverter 22 Front motor 23 Front water-cooled oil cooler 24 Front gearbox 25 Rear inverter 26 rear motor 27 Water-cooled oil cooler 28 rear gearbox 31 Pump 32 Reservoir tank 33 Radiator 35 Air-cooled oil cooler 36 Bypass valve 37 Oil pump 38 Tank 41 Control Unit 43 Storage section 50 Battery 51 rear tire 52 Side body 53 Undercover Tx switching temperature Tf, Tr distribution change temperature

Claims

1. A motor cooling method by a controller that controls a motor that drives an electric vehicle, comprising: an oil cooling circuit for cooling a rear motor that drives rear wheels of the electric vehicle is provided with a water-cooled oil cooler and an air-cooled oil cooler; When the temperature of the rear motor is lower than a predetermined switching temperature, the oil in the oil cooling circuit is circulated only through the water-cooled oil cooler, When the temperature of the rear motor is equal to or higher than the switching temperature, the oil in the oil cooling circuit is circulated to the water-cooled oil cooler and the air-cooled oil cooler. Motor cooling method.

2. The air-cooled oil cooler is installed rearward of the electric vehicle relative to the rear motor, and is cooled by airflow taken in from the bottom or side of the electric vehicle. The motor cooling method according to claim 1 .

3. the electric vehicle includes a transmission driven by the rear motor, The transmission is cooled by the oil cooling circuit, The switching temperature is set to a temperature at the boundary between a range in which the friction of the transmission increases as the oil temperature of the transmission decreases and a range in which the friction does not change even if the oil temperature of the transmission increases.

3. The motor cooling method according to claim 1 or 2.

4. the electric vehicle includes a front motor that drives front wheels of the electric vehicle and the rear motor; When the driving force of the electric vehicle reaches or exceeds a predetermined driving force threshold, the driving force distribution of the rear motor is made larger than the driving force distribution of the front motor. The motor cooling method according to claim 1 .

5. When the temperature of the front motor or the rear motor reaches or exceeds a predetermined distribution change temperature, the driving force distribution between the front motor and the rear motor is changed. The motor cooling method according to claim 4.

6. The water-cooled oil cooler is cooled by cooling water in a water-cooling circuit that cools a front power train including the front motor and a rear power train including the rear motor. The motor cooling method according to claim 4.

7. predicting a driving load applied to the electric vehicle according to preset driving conditions and calculating a predicted load; The distribution of driving force between the front motor and the rear motor is changed in accordance with the calculated predicted load. The motor cooling method according to claim 4.

8. A motor control device including a controller that controls a motor that drives an electric vehicle, an oil cooling circuit for cooling a rear motor that drives rear wheels of the electric vehicle is provided with a water-cooled oil cooler and an air-cooled oil cooler; The controller When the temperature of the rear motor is lower than a predetermined switching temperature, the oil in the oil cooling circuit is circulated only through the water-cooled oil cooler, When the temperature of the rear motor is equal to or higher than the switching temperature, the oil in the oil cooling circuit is circulated to the water-cooled oil cooler and the air-cooled oil cooler. Motor control device.

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